i recently bought a yamaha pc2002 amp that is quite old. the right channel seems to fade in and out with static and does not maintain a constant volume, although if wiggled the right way will work fine but soon dies out, the left channel works perfect. any ideas?

I have tried this, and all connections are good. if leaving it it will get to proper volume, stay for 5 minutes then go back to fading in and out. If the mixer is turned down and low input level it sounds fine but when the mixer is turned up the problem will be prominent. I have tried multiple mixers as well so it is not that, or the cd player, have used laptop etc.